The Animal Core was started in 1997 to accommodate the growing need of Center investigators for CF mice, with support from the Cystic Fibrosis Foundation, and in1 998, it received additional support from our new SCOR grant. However, the utilization of this Core kept growing and it is now proposed for inclusion in the CF Core Center. This Core has as its goals the provision of animals of various CF genotypes to CF investigators, the provision of genetically engineered animals of relevant genotypes apart from CF for CF-related investigations, the provision of the pseudomonas-agar bead model to Center investigators, and the training and assistance of technicians, trainees, and investigators in various aspects of mouse care, handling, medical procedure, and research procedures. The Core also serves as a focal point for communication among investigators about mouse issues and has been instrumental in minimizing the use of animals as research subjects by maximizing the utilize of each individual mouse for use by different investigators, if feasible. In order to meet its goal the Core performs such activities as breeding, backcrossing, genotyping, special husbandry activities required by the fragile condition of the CF mice, database and web page maintenance, liaison with the Animal Resource Center personnel and condition of the CF mice, database and web page maintenance, liaison with the Animal Resource Center personnel and management, monitoring of mice and early identification of difficulties, training and education. The Corer Director is Mitchell Drumm, Ph.D., himself a major user and a geneticist, and the Supervisor is Anna van Heeckeren, D.V.M., who is expert not only in mouse health but in the creation and standardization of the agar bead model. This Core, in its brief existence, has already supported more than a dozen funded investigators and the demand is growing.